Nutritional value of silage maize is related to the kinetics of ruminal fiber digestion. A maize population designated the Wisconsin Quality Synthetic (WQS) has undergone two cycles of S2-topcross recurrent selection that included selection for reduced neutral detergent fiber (NDF) and increased in vitro NDF digestibility (IVNDFD) measured after a 48 hour incubation in rumen fluid. We examined IVNDFD of the first two cycles of selection of WQS over multiple periods of incubation in rumen fluid to determine whether the selection protocol influenced rate and extent of fiber digestion.